1. Field of the Invention
The present invention relates to a ceramic sintered body which is employed for an electronic material such as an IC substrate material, a package material or the like, and more particularly, it relates to a colored aluminum nitride sintered body having high heat conductivity and a method of preparing the same.
2. Description of the Background Art
In recent years, the technique relating to a large-scale integrated circuit device (LSI) has made a marked advance with remarkable improvement in degree of integration. Following such improvement in degree of integration and increase in size of an IC chip, the heating value of a package carrying such an IC chip has also been improved. Accordingly, a heat radiation property of a substrate material employed for a package for a semiconductor device etc. has been regarded as important. The heat conductivity of an alumina sintered body, which has generally been widely applied to an IC substrate, is rather insufficient as to the heat radiation property. Thus, it is difficult for the alumina sintered body to cope with the increased heating value of the IC chip. To this end, study has been made in order to substitute beryllia, having high heat conductivity, for such an alumina sintered body. However, beryllia is hard to handle because of its toxicity.
On the other hand, a sintered body of aluminum nitride (AlN), which originally has high heat conductivity and high insulability with no toxicity, is watched with interest as a material for a circuit substrate or a package for a semiconductor device.
In general, an impurity content of such an AlN sintered body is so reduced as to obtain an AlN sintered body which is an excellent in heat conductivity and electrical insulability. Such a sintered body is also excellent in translucence, and hence the same is preferably applied to an optical filter etc. in practice. However, it is problematic to apply the AlN sintered body to a package etc. since transmission of ultraviolet rays leads to a malfunction of the IC.
To this end, various researches have been made as to colored AlN sintered bodies, and several successful examples have been reported.
For example, Japanese Patent Laying-Open No. 63-233079 discloses a black aluminum nitride sintered body and a method of preparing the same. According to this literature, a black AlN sintered body can be obtained by adding a specific amount of calcium tungstate powder and/or calcium molybdate powder to AlN powder, mixing and molding the same, and thereafter firing the mixture in a non-oxidizing atmosphere.
On the other hand, Japanese Patent laying-Open No. 63-310772 describes that a black AlN sintered body can be obtained by sintering AlN powder with metal molybdenum or a molybdenum compound, serving as an additive. However, the aluminum nitride sintered bodies disclosed in the aforementioned two gazettes have a low heat conductivity values of about 100 W/m.multidot.K.
AlN is apt to incorporates an impurity such as oxygen. Thus, AlN powder of high purity is generally employed in order to improve heat conductivity. If the aforementioned substance is added for coloring, therefore, heat conductivity may be reduced. Thus, it has been impossible to obtain a colored AlN sintered body having high heat conductivity.
However, a substrate material for carrying an IC chip having a high output must have a high heat conductivity, so that its heat radiation property is improved in order to prevent the IC from a malfunction caused by temperature rise of the IC chip. At the same time, the substrate must be colored in order to prevent the IC from a malfunction caused by transmission of ultraviolet rays. According to the conventional technique, however, it has been difficult to provide a ceramic substrate, which can simultaneously satisfy the two requirements for the substrate material for an IC chip, as hereinabove described.